Quote:
|
I didn't measure in series, but put the leads on the positive and negative terminals of the battery. I changed the alternator out this morning, and you are correct, I see the same cycle of numbers with about a 38V peak. I'm not sure how there are so many you tube videos showing the same test with completely different results, unless it is, as you said due to the accuracy of the autoranging feature.
|
The difference is merely where the tesprobes are attached to. I am willing to bet that some of the U-Tube videos are tested across the diode(s). In this case, you'll only measure the voltage drop across the diode e.g. anywhere between 0.3-0.8 Volts.
If you referenced to battery negative post, you'll measure the rectified voltage, which will increase, depending on where the positive test probe is attached to.
Quote:
|
So it appears the diodes in the old one were just fine. The bearings were shot though, and the new one is much quieter. The DC voltage is now 14.5V which is much higher than before, so the brushes were worn out as well.
|
Yes, I think you are right. They were just fine.
The higher voltage, however is probably related to the condition of the electrical system and / or the different voltage regulator. You could measure several times under different conditions (Lights on, Light Off etc.) and every time you would get a slightly different reading. The 14.5 Volts are possibly the maximum output voltage that the regulator allows. This is fine as long as it is only for a relatively short time.
The batteries nominal voltage is 12VDC, realistically you'll measure most of the time (engine off) about 12.6 - 12.8 Volts. During the starter cranking this voltage will probably drop close to 11.8 Volts but quickly will rise again after the engine started. Thats when the maximum alternator voltage should occur. This also means maximum current!
Quote:
|
I'm still scratching my head on the amperage reading. The first thing is I have to clamp it to the positive and negative wires to get any reading at all. I thought the clamp was only supposed to go over the positive wire. I have it in 400A DC mode. But either way, it still read in the mid 50s so that must be the max amps the car uses at full load. The textbook made the assumption that all cars must pull as many amps as the alternator is rated for.
|
When using the clamp in an AC measurement application, the current is going in one direction and changes into the other direction, depending on wave form, e.g. is alternating at the frequency of the AC.
Not knowing the design of your clamp meter, it is possible that it needs some supply voltage to function in DC mode at all.
In a DC measurement, the current flow is steady in one direction, there is no reference for it, so you'll have to provide a reference, since every electrical energy has to come back to the source. Some of it is dissipated and converted into heat, so it won't make it back as such.
A general rule of thumb when measuring electricity is to set the measuring device to the approximate and expected value. (That's easy to say for me) Measure devices will measure with a larger error if the range is to wide. For example: if I expect a 60 Amp current, I would select a 100 Amp range, if available. In this way the error is smaller than at 400 Amp range. In some case (autorange) the meter will select the range and it is out of your hands.
The text book is right and wrong at the same time.
If I would design a vehicles electrical system, I would start out, what is called a worst case scenario. The worst condition that can happen, that I have to consider. This doesn't mean that the system is always running at this condition.
So, I take all the consumer and I mean all of them!
Add all of them together and get an idea of how much current (Power) I have to provide for it to function under the worst condition. For example: if all consumer require a current of 50 Amps, I will give some room for short term higher consumer etc. and say, well a 72 Amp alternator should suffice. Of course, I would have to built in some protection, perhaps a 150 Amp fuse (the size of the fuse depends on the maximum rating of the alternator). The alternators absolute rating could be capable of supplying more current, but would destroy itself in the course.
So in your test you see the current that is currently required, but not the maximum.
Sorry for those long write ups, but this is a subject that can't be explained in a one liner!